1. Field of the Invention
The present invention relates to a viscoelasticity measuring apparatus that measures viscoelasticity of a measurement target.
2. Related Art
A measuring apparatus for measuring viscoelasticity of a measurement target such as human skin has been known heretofore (for example, Japanese Unexamined Patent Application Publication No. 2000-316818, hereinafter referred to as Patent Document 1). In the invention of Patent Document 1, a pressure sensor unit provided with a probe measures a pressure applied to the measurement target by driving a driving unit.
However, in the invention of Patent Document 1, since the driving unit drives the probe and the pressure sensor unit integrally, the driving unit structure is large and its weight is heavy. As a result, the influence of shaking of a measurer's hand holding the measuring apparatus on measuring precision of the pressure sensor becomes greater. In addition, the driving force of an actuator must be greater for the increased weight.
Furthermore, in the invention of Patent Document 1, the distance between the actuator and the probe is large due to the pressure sensor interposed therebetween. This increases axial runout of the actuator and the influence on measuring precision. Additional components such as bearing and coupling for controlling the shaking are thus required, leading to increased cost. The bearing generates slide friction and has an influence on measuring precision especially when handling low pressure.
Moreover, in the invention of Patent Document 1, a spring presses the pressure sensor to prevent shaking and the apparatus is fixed to a ball screw device, so that the sensor fixing state is unstable due to backlash and the like. In order to perform sensing of higher precision, the fixing state of the pressure sensor must be more stable.
For those reasons, the invention of Patent Document 1 is not suitable for high precision measurement that handles minute pressure.